exploring-codebases

exploring-codebases is a skill for Claude Code, Codex from oaustegard/claude-skills. It costs 209 tokens per session (2,394 once invoked), scanned A, original, MIT.

A guided first review of an unfamiliar software repository, meaning a project’s files and source code. It combines a structural scan of the code with a description of what the project does.

In plain words
What is it for?
Use it to set up the project environment, obtain a repository copy, map its structure, identify important code elements, and create an overview of its features.
Why use it?
It reduces the time needed to understand a codebase that no one on the team has worked in before. The fixed workflow also makes the initial investigation repeatable.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/oaustegard/claude-skills/exploring-codebases
Any agent
npx skills add oaustegard/claude-skills --skill exploring-codebases
Clone the repo
git clone --depth 1 https://github.com/oaustegard/claude-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for exploring-codebases

README.md
[![agentmods](https://agentmods.dev/badge/skills/oaustegard/claude-skills/exploring-codebases.svg)](https://agentmods.dev/skills/oaustegard/claude-skills/exploring-codebases)
Your own site
<a href="https://agentmods.dev/skills/oaustegard/claude-skills/exploring-codebases"><img src="https://agentmods.dev/badge/skills/oaustegard/claude-skills/exploring-codebases.svg" alt="Measured on agentmods" height="20"></a>
Per session 209 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,394 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00209 $0.02394
Opus 5 $0.00105 $0.01197
Sonnet 5 $0.00042 $0.00479
Haiku 4.5 $0.00021 $0.00239

Measured 6d ago against content hash ac625263fcfc, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

exploring-codebases scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl -sL -H "Authorization: Bearer $GH_TOKEN" \
exploring-codebases/SKILL.md · 210 lines

How it starts

The opening of the file, as written. The whole thing — 210 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Exploring Codebases

Exploratory code analysis for unfamiliar repositories. Orchestrates tree-sitting (structural) and featuring (semantic) over a local copy.

Workflow

Five numbered steps, in order. Do not skip step 0.

0. Setup (once per session)

uv venv /home/claude/.venv 2>/dev/null
uv pip install tree-sitter --python /home/claude/.venv/bin/python
export PYTHON=/home/claude/.venv/bin/python
export TREESIT=/mnt/skills/user/tree-sitting/scripts/treesit.py
export GATHER=/mnt/skills/user/featuring/scripts/gather.py

If step 2's --stats reports Symbols: 0 on a repo you know contains code, the tree-sitter core package isn't installed — come back here and install it (the engine bundles its own grammars and does NOT use tree-sitter-language-pack). Treesit exits 0 and prints no error in that case, so zero symbols is the only signal you get. There is no Errors: line: that one appears for parse failures, and an absent parser never reaches parsing. The full signal, and the 2026-08-24 measurement behind it, is in the tree-sitting skill's Setup section.

1. Get the repo (tarball, not per-file)

OWNER=...
REPO=...
REF=main                    # branch name, tag, or SHA. For a PR: pull/N/head
curl -sL -H "Authorization: Bearer $GH_TOKEN" \
  "https://api.github.com/repos/$OWNER/$REPO/tarball/$REF" -o /tmp/$REPO.tar.gz
mkdir -p /tmp/$REPO && tar -xzf /tmp/$REPO.tar.gz -C /tmp/$REPO --strip-components=1
ls /tmp/$REPO | head        # sanity check — did extraction land?

One HTTP call gets the whole repo. Do NOT curl README, cat files, or fetch via contents/PATH first — they're in the tarball. The Authorization header is only needed for private repos; public repos work without it.

Ref selection matters. If exploring a feature branch, PR, or tag, set REF accordingly. The default main will silently give you stale code if the question is about an unmerged branch.

2. Structural scan

$PYTHON $TREESIT /tmp/$REPO --stats

Read the full file on GitHub · 210 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 6d ago First seen · 210 lines · 209 tokens per session scan A ac625263fcfc

Subscribe to this mod's changes

exploring-codebases is a skill published in the GitHub repository oaustegard/claude-skills (147 stars, last pushed yesterday), licensed MIT. It adds 209 tokens to every session and 2,394 once invoked, about $0.0010 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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